PHOENIX (KSAZ) - Each year, Phoenix Police impounds approximately 5,000 firearms, with most being booked as evidence connected to criminal incidents.
The person in possession of the firearm when it was confiscated might not admit to be actual crimes the gun was used in, but each gun's shell casings leave behind important clues for investigators to follow.
"It s very similar to, like, a fingerprint," said Jessica Ellefritz with Phoenix Police. "There are certain tool marks left behind on a casing when a gun is fired."
Every month, Phoenix Police fires off around 400 evidence guns, including rifles. The casings are then brought back to the lab, where high-definition photos are taken of the markings.
Those photos are then entered into NIBIN - National Integrated Ballistic Information Network, where the evidence will then be compared to casings collected in other crimes.
"At any given time, there's a firearm sitting on a shelf at the police impound that could be the murder weapon from another homicide," said Ellefritz. "Unless we test fire that and have those casings, we may never know that that gun was involved in a homicide."
Ellefritz went on to say the department has found as many as 120 matches in one month, via the method of comparing shell casings. So far, the most notable success story is that of a bank robber who was shot and killed in Phoenix back in 2013 that has since been linked to the shooting death of an officer in another state.
"The gun that he had that day, we were able to test fire it, get the casing in the system, and we were able to match those to the casings entered by law enforcement in Mississippi," said Ellefritz.